(i) `text(Preparation)` :

(a) Gossage process : `underset(10 % solution)(Na_2CO_3) + Ca (OH)_2 -> 2Na OH downarrow + CaCO_3`.

(b) Eleccrolytic method : Caustic soda is manufactured by the electrolysis of a concentrated solution of `NaCl`.

At anode: `Cl^(-)` discharged; At cathode: `Na ^(+)` discharged

(c) Castner-Kellener cell (Mercury cathode process) : `NaOH` obtained by electrolysis of aq. solution of brine. The cell comprises of rectangular iron tank divided into three compartments.

Outer compartment - Brine solution is electrolysed ; Central compartment- `2%` `NaOH` solution and `H_2`.

(ii) `text(Properties)` : White crystalline solid, highly soluble in water. It is only sparingly soluble in alcohol.

(a) Reaction with salt : `FeCl_2 + 3NaOH -> undersettext(Insoluble hydroxide)(Fe(OH)_3) downarrow + 3 NaCl`

`HgCl_2 +2NaOH -> undersettext(unstable)[Hg(OH)_2] + H_2O +undersettext(yellow)(HgO) downarrow`

`AgNO_3 +2NaOH -> 2NaNO_3 +2AgOH -> undersettext(Brown)(Ag_2O) downarrow + H_2O`

`text(Note)` : `Zn`, `Al`, `Sb`, `Pb`, `Sn` and `As` from insoluble hydroxide which dissolve in excess of `NaOH` (amphoteric hydroxide .)

`NH_4Cl + NaOH oversettext(heat)-> NaCl + NH_3 uparrow +H_2O`

(b) Reaction with halogens : `X_2 + 2NaOH` (cold) `-> NaX + undersettext(sodium hypohalite)(NaXO +H_2O)`

`3X_2 + 6NaOH` (hot) `-> 5NaX + undersettext(Sod. halate)(NaXO_3) + 3 H_2O ; (X-Cl, Br, I)`

(c) Reaction with metals : Weakly electropositive metals like `Zn`, `Al` and `Sn` , etc.

`Zn +2 NaOH -> Na_2ZnO_2 + H_2 uparrow`

(d) Reaction with sand, `SiO_2` : `2NaOH +CO overset(150-200^oC)-> undersettext(Sod, formate)(HCOONa)`

(e) Reaction with `CO` : `2NaOH +CO overset(150-200^oC)-> undersettext(Sod. formate)(HCOONa)`

Note : `NaOH` breaks down the proteins of the skin flesh to a pasty mass, therefore it is commonly known as caustic soda.

(iii) Uses : In the manufacturing of sodium metal, soap, rayon, paper, dyes and drugs. For mercuring cotton to make cloth unshrinkable and reagent in lab.

(i) `text(Preparation)` : Solvay process : In this process, brine `(NaCl)` and `CO_2` are the raw materials.

`NH_3 +CO_2 +H_2O -> NH_4HCO_3`

`NH_4HCO_3 +NaCl overset(30^oC)-> NaHCO_3 downarrow +NH_4Cl `

`2NaHCO_3 overset(250^oC)-> Na_2CO_3 + H_2O + CO_2`

`NH_4Cl + undersettext(slaked lime)(Ca(OH)_2) -> CaCl_2 + 2H_2O + 2NH_3`

Note : `NaCl` so formed in the above reaction is a by product of solvay process.

(ii) `text(Properties)` : (a) `Na_2CO_3*10H_2O oversettext(dry air)-> undersettext(Monohydrate)(Na_2CO_3*H_2O) + 9H_2O`

`Na_2CO_3H_2O overset(Delta)-> Na_2CO_3 ->` It does not decompose on further heating even to redness(m pt. `853^oC`)

(b) It is soluble in water with considerable evolution of heat.

`Na_2CO_3 + H_2O -> undersettext(weak acid)(H_2CO_3) + 2Na^(+) + 2OH^(-)`

(c) It is readily decomposed by acids with the evolution of `CO_2` gas.

(d) `Na_2CO_3 + H_2O + CO_2 -> 2NaHCO_3`

(iii) `text(Uses)` : In textile and petroleum refining, Manufacturing of glass, `NaOH` soap powders etc

(i) `text(Preparation)` : It is manufactured by heating sodium metal on aluminium trays in air(free from `CO_2`)

`2Na + O_2 ` (air) `overset(Delta)-> Na_2O_2`

(ii) `text(Properties)` : (a) When pure it is colourless. The faint yellow colour of commercial product is due to presence of small amount of superoxide `(NaO_2)`.

(b) On coming with moist air it become white due to formation of `NaOH` and `Na_2CO_3`

`2Na_2O_2 + 2H_2O -> 2NaOH +O_2`; `2NaOH +CO_2 -> Na_2CO_3 +H_2O`

(c) It is powerful oxidising agent. It oxidises `Cr(III)` hydroxide to sodium chromate, `Mn(II)` to sodium manganate and sulphides to sulphates.

(iii) `text(Uses)` : As a bleaching agent and it is used for the purification of air in confined spaces such as submarines because it can combine with `CO_2`, to give `Na_2CO_3` and oxygen, `2CO_2 +2NaO_2 -> 2Na_2CO_3 +O_2`

`text(Preparation)` : By heating sodium nitrite with metallic sodium, or sodium azide `(NaN_3)` with sodium nitrite.

`2NaNO_2 + 6Na -> 4Na_2O + N_2`

`3NaN_3 + NaNO_2 -> 2Na_2O + 5N_2`

`text(Properties)` :

(a) `Na_2O` is a white amorphous substance. It reacts with water violently forming `NaOH`.

(b) On heating above `400-C`, it disproportionates to give peroxide and metallic sodium.

`Na_2O + H_2O _> 2NaOH`

`2Na_2O overset(400^oC)-> Na_2O_2 + 2Na`

(c) It reacts with liquid ammonia forming sodamide and `NaOH`.

`Na_2O + NH_3 -> NaOH + NaNH_2`

`text(Uses)` : It is used as a dehydrating and polymerising agent in organic chemistry.

`text(Preparation)` : (i) It is obtained as the intermediate product in the solvay ammonia soda process.

(ii) Normal carbonate can be changed to bicarbonate by passing carbon dioxide through its saturated solution.

`Na_2CO_3+CO_2+H_2O-> undersettext(Sparingly soluble)(2NaHCO_3)`

`text(Properties)` : (i) `NaHCO_3` is a white crystalline solid, sparingly soluble in water.

(ii) The solution is alkaline in narure due to hydrolysis.

`NaHCO_3 + H_2O-> NaOH + H_2CO_3`

Its aqueous solution gives yellow colour with methyl orange but no colour with phenolphthalein and thus weak base.

(iii) On heating, it loses carbon dioxide and water forming sodium carbonate.

`2NaHCO_3-> Na_2CO_3 + H_2O + CO_2`

(iv) The metal salt which forms basic carbonate with sodium carbonate, gives normal carbonate with sodium bicarbonate.

`ZnSO_4 + 2NaHCO_3 -> ZnCO_3 + Na_2SO_4 + H_2O + CO_2`

`text(Uses)` : `NaHCO_3` is

(i) as a medicine (soda bicarb) to neutralise the acidity in the stomach.

(ii) in making effervescent drinks.

(iii) for making baking powder. Baking powder is a mixture of potassium hydrogen tartrate and sodium bicarbonate.

(iv) for production of carbon dioxide.

(v) in fire extinguishers.

Sodium chloride is the most common salt of sodium. It is also called sea salt.

Manufacture from sea water : The sea water is allowed to dry up under summer heat in small tanks or pits. The solid crust of `NaCl` so formed is collected. Sodium chloride thus obtained contains impurities like magnesium chloride, calcium chloride etc. It is ptuified by passing hydrogen chloride through a saturated solution of the commercial salt. The precipitation of sodium chloride occurs due to common ion effect.

`text(Properties)` :

(a) It is a white crystalline solid soluble in water. It dissolves in water with absorption of heat.

(b) It is insoluble in alcohol.

(c) The common salt is the starting material for the preparation of all the other sodium compounds e.g. `NaOH, Na_2CO_3, NaHCO_3` etc. and extraction of sodium.

`text(Uses)` : `NaCl` is used as

(i) an essential constituent of food.

(ii) a preservative of food articles like fish, meat etc.

(iii) for making useful sodium compounds.

(iv) in salting out of soap, and in making freezing mixtures.

Pure `NaCl` is not hygroscopic. It shows hygroscopic nature due to impurities.

Preparation of Salt cake : (i) The anhydrous sodium sulphate (salt cake) is obtained as a by-product in the manufacture of hydrochloric acid.

(ii) Salt cake is also produced during the manufacture of sodium carbonate when `NaCl` is heated w'ith `H_2SO_4`.

(iii) Now-a-days, it is manufactured by heating `NaCl` with sod. bisulphate (nitre cake). Nitre cake is obtained by the action of `H_2SO_4` on sodium nitrate (Chile saltpetre).

`undersettext(Chile saltpeter )(NaNO_3) + H_2SO_4 -> undersettext(Nitre cake)(NaHSO_4) + HNO_3`

`undersettext(Nitre cake)(NaCl) + NaHSO_4 -> undersettext(Salt cake)(Na_2SO_4) + HCl uparrow`

Preparation of Glauber's salt, `Na_2SO_4.10H_2O :` The salt cake `(Na_2SO_4)` is dissolved in water and the solution is subjected for crystallization. Below `32-C`, the decahydrate salt crystallises out from the aqueous solution. Above `32-C` the anhydrous salt separates. Saturated solution of the decahydrate, on cooling below `12-C`, gives crystals of heptahydrare.

`text(Properties)` :

(i) The decahydrate effloresces in dry air forming the anhydrous salt. It is a crystalline solid, soluble in water.

(ii) On treatment with lead, barium or strontium salts, it forms the corresponding insoluble sulphate, e.g.

`Pb(NO_3)_2 + Na_2SO_4 -> PbSO_4 downarrow + 2NaNO_3`

(iii) When a solution having equivalent quantity of anhydrous `Na_2SO_4` and conc. `H_2SO_4` is cooled, prismatic crystals of sodium bisulphate (sodium hydrogen sulphate, `NaHSO_4` ) are formed.

`Na_2 SO_4 +H_2SO_4 -> 2NaHSO_4`

(iv) On heating with carbon it is reduced to sod. sulphide.

`Na_2SO_4 + 4C -> Na_2S +4 CO`

`text(Uses)` : Sodium sulphate is used :

(i) in the manufacture of craft paper (brown paper for wrapping, etc.) and paper board,

(ii) in the manufacture of window glass,

(iii) as mild laxative (in medicine) and

(iv) in the preparation of `Na_2S, Na_2S_2O_3` and `NaHSO_4`. sod. bisulphate is an acidic salt in solution and can be used in place of sulphuric acid. For example, `Al_2O_3`, which is not attacked by `H_2SO_4`, may be converted into sulphate when fused with sodium hydrogen sulphate.

`Al_2O_3 + 6NaHSO_4 -> Al_2(SO_4)_3 + 3Na_2SO_4 + 3H_2O`

The important minerals of potassium are :

(i) Carnallite `: KCl*MgCl_2*6H_2O`

(ii) Kainite `: KCl*MgSO_4*MgCl_2*3H_2O`

(iii) Indian salt peter : `KNO_3`

(iv) Felspar: `K_2O*Al_2O_3*6SiO_2` or `(KAlSi_3O_8)`

(6) Sylvine : `KCl`

`text(Preparation or Extraction)` : Metallic potassium is not of much demand because cheaper sodium metal serves almost all the purposes where potassium metal is needed. However it can be prepared by :

(i)heating potassium carbonate with coke.

`2K_2CO_3 + C -> 4K + 3CO_2`

(ii) electrolysing fused `KCl` alongwith little `KF` or `CaCl_2`.

(iii) heating potassium fluoride with calcium carbide.

`2KF + CaC_2 overset(1000^oC)-> 2K + CaF_2 + 2C`

`text(Properties)` :

(i) It is silvery white metal resembles with sodium in its physical and chemical properties.

(ii) It is lighter, softer and more reactive than sodium.

(iii) It reacts violently with water with evolution of huge amount of energy so that hydrogen evolved catches fire.

(iv) lt has three isotopes of mass no. `39`, `40`, `41`, the former is most abundant. `K^(40)` is radioactive and `beta` emitter.

`text(Uses)` : `K` is used in

(i) Photo electric cell because of low IP values (`Na` and `Li` are not used). `Cs` is also used in photo electric cell.

(ii) An alloy of `K` and `Na` is liquid at room temperature and is used in special thermometers used for finding temperature above b.pt. of `Hg`.

`text(Oxides)`

Three oxides of potassium are known :

(i) potassium monoxide (potassium oxide), `K_2O`;

(ii) potassium dioxide (tetroxide or super oxide), `KO_2` or `K_2O_4 ;` and

(iii) potassium sesquioxide, `K_2O_3`.

`text(Preparation)` :

(a) `4K` (excess) `+ O_2 undersettext(Reduced pressure) overset(180^oC) -> undersettext(Pot. monoxide)(2K_2O)`

`2KOH + 2K oversettext(heat)-> 2K_2O +H_2`

(b) `K + O_2 text[(excess)] oversettext(burning)-> undersettext(Pot.dioxide)(KO_2)`

`2KOH + O_3 -> undersettext(dry)(2KO_2) + H_2O`

(c) `4K` (dissolved in liq. `NH_3`) `overset(3O_2)-> undersettext(Pot. sesquioxide)(2K_2O_3)`

`text(Properties)` :

(i) Potassium monoxide is a white hygroscopic solid while potassium dioxide is a chrome yellow powder.

(ii) Potassium monoxide and dioxides on hydrolysis form `KOH`.

`K_2O + H_2O -> 2KOH`

`2KO_2 + 2H_2O -> 2KOH + H_2O_2 + O_2`

(iii) `KO_2` on heating with sulphur forms potassium sulphate.

`2KO_2 + S -> K_2SO_4.`

It is manufactured like that of `NaOH`, i.e. by the electrolysis of `KCl` solution or by the action of lime on potassium carbonate. It can also be obtained by the action of baryta, `Ba(OH)_2` on potassium sulphate.

`K_2SO_4 + Ba(OH)_2 -> BaSO_4 downarrow + 2KOH`

`text(Properties)` : `KOH` has properties similar to those of sodium hydroxide. However, it is a stronger alkali and more soluble in alcohol and is, therefore used in organic reactions instead of caustic soda, as well as it is a better absorber of `CO_2` than `NaOH` because potassium carbonate is more soluble in water. Its aqueous solution is known as potash lye.

`text(Uses)` : Potassium hydroxide is used :

(i) for the absorption of `CO_2` and `SO_2`,

(ii) in the manufacture of soft soap,

(iii) in the form of alcoholic solution (alcoholic caustic potash) in organic chemistry for elimination reagent.

`C_2H_5Br + KOH text(alc.) -> C_2H_4 + KBr + H_2O`

`C_2H_5Br + KOH text(aq.) -> C_2H_5OH + KBr`

(iv) for drying gases since it is extremely deliquescent.

`text(Preparation)` : It is noted here that unlike sodium carbonate, potassium carbonate cannot be prepared by the solvay method because potassium bicarbonate, being highly soluble in water, would not be precipitated out.

(i) `text(Leblanc process)` : Potassitun chloride of carnallite is converted into `K_2SO_4` which is then heated with coal and limestone to give `K_2CO_3`.

`KCl + H_2SO_4 -> KHSO_4 +HCl`

`KCl +KHSO_4 -> K_2SO_4 + HCl`

`K_2SO_4 +2C +CaCO_3 -> K_2CO_3 +CaS +2CO_2 uparrow`

(ii) `text(Precht process)` (Magnesia process) : In this process carbon dioxide is passed into a solution of `KCl` at `20-C` in the presence of hydrated magnesium carbonate to give potassium magnesium hydrogen carbonate.

`2KCl + 3[MgCO_3*3H_2O] + CO_2 -> 2[KHCO_3*MgCO_3*4H_2O] downarrow + MgCl_2`

Potassium magnesium hydrogen carbonate is taken out and decomposed by either of the following methods.

(a) It is heated at `140-C` under pressure to give `K_2CO_3.`

`2[KHCO_3*MgCO_3*4H_2O] overset(140^oC)-> K_2CO_3 + 2MgCO_3 downarrow + CO_2 uparrow + 9H_2O uparrow`

(b) It is treated with a suspension of magnesium oxide in water below `20-C`.

`2[KHCO_3*MgCO_3*4H_2O] + MgO -> undersettext(Hydrated magn. carbonate)[3(MgCO_3*3H_2O)] downarrow + K_2CO_3`

Magnesium carbonate, obtained in either of the method, is removed and used again.

`text(Properties)` : It is a white deliquescent powder readily soluble in water. It forms fusion mixture when mixed with sodium carbonate. It resembles sodium carbonate in most of its reactions. However, it is more alkaline and more soluble in water than sodium carbonate. On heating with steam to redness, it is decomposed to give `KOH`.

`K_2CO_3 + H_2O text[(steam)] -> 2KOH + CO_2 uparrow`

`text(Uses)` : Potassium carbonate is used :

(i) as fusion mixture (equimolecular quantities of `Na_2CO_3` and `K_2CO_3`) which fuses at low temperature than either of the constituents.

(ii) in the manufacture of soft soap (toilet soaps), hard glass and various potassium compounds.

(iii) in washing wool and

(iv) as a drying agent in the laboratory.

By passing `CO_2` through a cold saturated solution of potassium carbonate, `KHCO_3` is obtained.

`K_2CO_3 + H_2O +CO_2 -> KHCO_3`

Properties and Uses : It resembles sodium bicarbonate in all properties except that it is more soluble in water. It is used in medicine and in baking powders.

`text(Preparation)` : (i) By treating `KCl` or `KOH` with `H_2SO_4`.

`KCl + H_2SO_4 -> K_2SO_4 + 2HCl`

`KOH + H_2SO_4 -> K_2SO_4 + 2H_2O`

(ii) By heating naturally-occuring mineral schonite(`K_2SO_4*MgSO_4*6H_2O`) with sylvine (`KCl`).

`K_2SO_4 * MgSO_4*6H_2O + 2KCl underset(Delta)-> 2K_2SO_4 + MgCl_3 + 6H_2O`

(iii) By heating dry `KO_2` with sulphur

`undersettext(dry)(2KO_2) + S underset(Delta) -> K_2SO_4`

`text(Properties)` :

(i) It is a white crystalline solid, not very soluble in water.

(ii) Its crystals do not contain water of crystallization.

(iii) When heated with carbon, it is reduced to potassium sulphide.

(iv) It forms a series of double salts with the sulphates of trivalent metals, e.g. potash alum, `K_2SO_4*Al_2(SO_4)_3*24H_2O`.

`text(Uses)` :

(i) It is used as a fertiliser for tobacco and wheat.

(ii) for the manufacture of potash alum and glass.

(iii) as a purgative I medicine.

`text(Preparation)` :

(i) It is obtained by the action of `HI` on potassium hydroxide or potassium carbonate.

`KOH + HI -> KI + H_2O`

`K_2CO_3 + 2HI -> 2KI + CO_2 + H_2O`

(ii) It may also be prepared by heating iodine with hot and concentrated solution of potassium hydroxide. The resulting liquid (consists of `KI` and `KIO_3`) is evaporated to dryness and the solid residue is then ignited with powdered charcoal to convert iodate also into iodide.

`3I_2 + 6KOH -> 5KI + KIO_3 + 3H_2O`

`KIO_3 + 3C -> KI + 3CO`

The mass is extracted out with water, filtered and the clear solution is evaporated to dryness.

(iii) Potassium iodide is manufactured by the action of ferroso ferric iodide on potassium carbonate. The solution is boiled.

`4K_2CO_3 + Fe_3I_8 + 4H_2O -> undersettext(ppt.)(8KI) + 4CO_2 + Fe(OH)_2*2Fe(OH)_3`

`[Fe_3I_8` is formed separately by adding iodine to iron fillings in water]

`Fe + I_2 -> FeI_2`

`3FeI_2 + I_2 -> Fe_3I_8` (ferroso ferric iodide)

The precipitate is filtered out and the clear filtrate on crystallization gives crystals of potassium iodide.

`KBr`, potassium bromide can also be obtained similarly.

`text(Properties)` :

(a) It is a white crystalline solid, highly soluble in water and alcohol.

(b) It dissolves free iodine and forms potassium triiodide and thus solubility of iodide and thus solubility of iodine increases in presence of potassium iodide.

`KI + I_2 -> KI_3 -> KI + I_2`

`KI_2` is unstable and gives up extra iodine readily.

(c) Sulphuric acid decomposes potassium iodide to `I_2`.

`2KI +H_2SO_4 -> K_2SO_4 +2HI`

`2HI + H_2SO_4 -> 2H_2O + I_2 + SO_2`

`2KI + 2H_2SO_4 -> 2K_2SO_4 + I_2 + SO_2 + 2H_2O`

or `2KI + 3H_2SO_4 -> 2KHSO_4 + I_2 + SO_2 + 2H_2O`

(d) `F_2`, `Cl_2`, `Br_2` liberate iodine from potassium iodide solution.

`2KI + Cl_2 -> 2KCl + I_2`

(e) It acts as a reducing agent. Acidified `KMnO_4,` acidified `K_2Cr_2O_7, HNO_3, H_2O_2, CuSO_4` etc. (oxidants) liberate iodine from `KI`.

(i) `K_2Cr_2O_7 + 4H_2SO_4 -> K_2SO_4 + Cr_2(SO_4)_3 + 4H_2O + 3O`

`ul([2KI + H_2SO_4 + O -> K_2SO_4 + K_2SO_4 + H_2O + I_2] xx 3)`

`6KI + K_2Cr_2O_7 + 7H_2SO_4 -> 4K_2SO_4 + Cr_2(SO_4)_3 + 3I_2 + 7H_2O`


(ii) `2KMnO_4 + 3H_2SO_4 -> K_2SO_4 + 2MnSO_4 + 3H_2O + 5O`

`ul([2KI + H_2SO_4 + O -> K_2SO_4 + H_2O + I_2] xx5)`

`2KMnO_4 +10KI + 8H_2SO_4 -> 6K_2SO_4 + 2MnSO_4 + 5I_2 + 8H_2O`

(iii) `2HNO_3 -> H_2O + 2NO_2 + O`

`ul(2KI + 2HNO_3 + O -> 2KNO_3 + I_2 + H_2O)`

`2KI + 4HNO_3 -> 2KNO_3 +2NO_2 +I_2 +2H_2O`

(iv) `[CuSO_4 +2KI -> undersettext(Unstable)(CuI_2) +K_2SO_4] xx2`

`ul(2CuI_2 -> Cu_2I_2 + I_2)`

`2CuSO_4 +2KI -> undersettext(Cuprous iodide)(Cu_2I_2) + 2K_2SO_4 +I_2`

(f) Potassium iodide forms insoluble iodides with `AgNO_3` and lead salts.

`AgNO_3 + KI -> undersettext(Yellow)(AgI) + KNO_3`

`Pb(CH_3COO)_2 + 2KI -> undersettext(Yellow)(PbI_2) + 2CH_3COOK`

(g) It forms a red precipitate with `HgCl_2` which dissolves in excess of potassium iodide forming potassium mercuric iodide.

`HgCl_2 + 2KI -> HgI_2 + 2KCl`

`HgI_2 + 2KI -> K_2HgI_4`

The alkaline solution of `K_2HgI_4` is called Nessler's reagent and used for the detection and estimation of `NH_4^(+)` ion.

`text(Uses:)` It is used

(a) as a solvent of iodine.

(b) as a reagent in laboratory.

(c) in medicine and photography.

(d) for making Nessler's reagent in the laboratory.